In many industries, both military and commercial, such as the aircraft, automotive, and appliance industries, wire bundles, or harnesses, are used extensively in the manufacturing processes of various products. Each bundle, or harness, generally comprises two or more wires that customarily are tied together at various points along their lengths to help ensure safety and durability, as well as a generally clean design.
Individually tying the bundle points by hand is costly, labor-intensive, and time-consuming, and often leads to carpal tunnel syndrome, or other physical injury, in the operator. With these problems in mind, several patented inventions have been directed toward automating the wire-tying process. One such device, that described in German Offenlegungsschrift U.S. Pat. No. 2,533,640 and improved in U.S. Pat. No. 4,558,894 to Detterbeck et al, is a hand-held pistol-like apparatus that forms a continuous crocheted tying structure around and along a bundle of wires. Even Detterbeck's improvement, however, does not actually tie a knot around the bundle: it simply pulls taut a predetermined number of loops. The device, therefore, is limited because it is not capable of tying individual knots at discrete points along the bundle.
Another patented device is described in U.S. Pat. No. 4,094,342 to Nishikawa et al. Nishikawa's device uses guide channels along the inside surface of the bundle holding elements to guide the string or cord around the wire bundle into the shape of a knot. The string is then pulled taut and cut. Several problems, including jamming and inconsistent knot quality, are associated with the Nishikawa device because it pushes, rather than pulls, the string around the bundle.
One feature of knot-tying is that a second pass of the string around the bundle must be laid in front of or behind a first pass. The prior art has not dealt with this problem very successfully; instead, prior art devices have tried simply to lay the string in patterns described by guide channels in the holding elements themselves. The Nishikawa device, and other devices, particularly the one described in U.S. Pat. No. 3,057,648 to Schwarze et al, use guide channels of differing depths to result in criss-crossing passes of the string. In a different approach, the device disclosed in prior art patent to Jung et al., U.S. Pat. No. 4,502,905, uses a transverse pin with a hook to grab the second pass of the string and draw it back across the first pass.
The Jung device illustrates another problem in the prior art--that of finishing the knot. After the string is laid around the bundle, the Jung device heats and bonds the string instead of tying a knot. Such heating, or other type of fusing or bonding, as well as the use of plastic, generic cotton string, or other fabric are frequently not acceptable because of the harsh environments encountered by many installations of wire bundles. Depending upon the particular industry and the application of the product, these bundles may be placed in environments of extreme temperature, vibration, radiation, or other types of shock. To withstand these conditions while maintaining the integrity of the knot, many applications require the use of "lace," a particular type of flexible string-like material.